1. Field of the Invention
The present invention relates to an alternating current generator. More particularly, it relates to an improvement of the cooling means of an alternating current generator which can effectively cool a rectifying device and a stator coil emitting a large heat energy.
2. Description of the Prior Art
The conventional alternating current generator will be described with reference to FIG. 1.
In FIG. 1, the reference numeral (1) designates a cooling fan driven by an engine (not shown); (2) designates a front bracket which is placed adjacent the cooling fan and has a cup-like shape having a cylindrical portion (2a); (21) designates a ventilating hole as the third ventilating hole which is formed in the end portion in the axial direction of the front bracket; (300) designates a cup-like rear bracket which is placed to face the front bracket in the axial direction and has a cylindrical portion (300a) and a dust-proof cylindrical portion (300b); (301) designates a ventilating hole as the first ventilating hole which is formed in the end portion in the axial direction of the rear bracket; (4) designates a stator held by the front and rear brackets (2), (300); (4a) designates a stator core which forms the stator; (5) designates a rotor placed inside of the stator and is rotatably held by the brackets (2), (300); (6) designates a rectifying device fixed to the rear bracket (300); (6a) designates a heat-radiating plate as a part of the rectifying device (6); (7) designates a stator coil which is wound in the stator and is impregnated with an insulating substrate such as varnish to be cured and (8) designates a collecting device for feeding current to the rotor (5).
In the structure as shown in FIG. 1, a coolant air enters from the outside of the rear bracket (300) by the revolution of the cooling fan (1) in the direction of the arrow mark (a) to cool the rectifying device (6), the stator coil (7), the stator core (4a) and the rotor (5).
The condition of passing the coolant air through the surface of the stator coil (7) and the stator core (4a) will be described with reference to FIG. 1.
In the stator coil (7) projecting toward the rear bracket (300) from the level of the stator core (4a), the reference numeral (7a) designates the surface of the stator coil (7) which faces the inner surface of the rear bracket (300) and (7b) designates the surface of the stator coil (7) which faces the rotor (5). Similarly, in the stator coil (7) projecting toward the front bracket (2), the reference numeral (7c) designates the surface of the stator coil (7) which faces the inner surface of the front bracket (2) and (7d) designates the surface of the stator coil (7) which faces the rotor (5). The reference numerals (71), (72) respectively designate air gaps formed between the stator coil (7) and the stator core (4a) when the stator coil is formed in the stator core (4a).
In the conventional generator having the structure shown in FIG. 1, the coolant air is introduced by revolution of the cooling fan (1) through the ventilating hole (301) of the rear bracket (300) and is passed through the rear bracket (300) in the direction of the arrow mark (a) to cool the surface (7b) of the stator coil (7) which faces the rotor (5) in the rear bracket side, the rotor (5), the stator core (4) and the surface of the stator coil (7) which faces the rotor in the front bracket side. However, on the surfaces (7a), (7c) of the stator coil (7) which face the inner surfaces of the front and rear brackets (2), (300) and in the air gaps (71) and (72), flowing of the cooling air is extremely small and a hot air stays in the portions to cause inferior heat radiation whereby the cooling of the stator coil is prevented. Thus, high temperature rising causes the problem on dynamo characteristic.